(a) Field of the Invention
The present invention relates to water soluble dithioesters capable of acting as chain transfer agents in preparing a vinyl-based polymer to control the molecular weight and the molecular weight distribution thereof, as well as being capable of living polymerization even in an aqueous solution, and a method for polymerization thereof.
(b) Description of the Related Art
A living polymerization process has characteristics of a living polymerization system in that it is capable of controlling a resultant polymer to a higher level, and particularly of controlling the resultant polymer within a narrow molecular weight distribution and controlling the length and the composition of at least one monomer by adjusting the reaction condition and the reaction conversion rate.
Solomon et al. first introduced living free-radical polymerization by using a nitroxide-based stable radical in order to control a polymerization reaction, in U.S. Pat. No. 4,581,429. Based on this approach, Georges et al. disclosed living radical polymerization in which the resultant polymer-has an increased average molecular weight as the yield increases when the polymerization is carried out at a higher temperature, so that the molecular weight is narrowly distributed (Macromolecules 26, 2987 (1993)). Nonetheless, this polymerization has problems in that the available monomer is limited and a condition of high temperature, is required. Further, Matyjasewski et al. disclose a living radical polymerization system in which atoms are transferred by using a metal complex, which is successfully practiced with acryl- and styrene-based monomers. Even so, commercial utilization of this polymerization system is limited since residual metals are produced. Therefore, introduction of a novel polymerization process is still required in order to overcome the above-mentioned problems.
Moad et al. also disclosed successful living polymerization by using a dithioester-based organic material, in Macromolecules 31, 5559 (1998) and WO 98/01478. This method, however, has problems in that the yield is excessively low since dithiobenzoic salt/acid is difficult to react with a halide compound and it is difficult to use various halogen compounds.
Unlike the above synthetic processes, WO 99/05099, WO 99/31144, Tetrahedron letters 40, 2435-2438, 1999, and Tetrahedron letters 40, 277-280, 1999 disclose a synthetic method of various dithioesters by using a radical termination reaction between dithiobenzoyl disulfide and an azo-based initiator, and living polymerization using the obtained compound.
Although the diverse approaches involve dithioesters, provision of water soluble dithioesters is still demanded.